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STRUCTURAL ARCHITECTURE AND EVOLUTION OF THE HUMBER ARM ALLOCHTHON, FRENCHMAN'S COVE - YORK HARBOUR, BAY OF ISLANDS,

NEWFOUNDLAND

St. John's

by

© Christopher R. Buchanan

A thesis submitted to the School of Graduate Studies in partial fulfillment of the

requirements for the degree of Ma.Ster of Science

Department of Earth Sciences Memorial University of Newfoundland

January,2004

Newfoundland

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Abstract

The Frenchman's Cove -York Harbour area provides extensive exposure of a critical structural contact within the Humber Arm Allochthon. The Blow Me Down Ophiolite Massif is exposed in the uppermost structural slice and complexly deformed and dismembered sedimentary rocks of the Humber Arm Supergroup are located in the intermediate slices of the allochthon. The sedimentary rocks are early Cambrian- to early Ordovician-age and represent diverse depositional settings, including early rift-basins, the continental slope of the Cambro-Ordovician carbonate platform, and syntectonic flysch deposits.

Five tectono-stratigraphic domains are distinguished on the basis of lithostratigraphy, the geometries of fold-thrust systems, and overprinting criteria of successive generations of structures. Detailed analysis of the fold-fault systems demonstrates that four phases of deformation affect the area. D 1 forms recumbent F 1

folds and duplex structures, creating regional scale nappe-type structures. A regional scale F2 antiformal culmination at Frenchman's Cove is associated with thrust faults that dismember folded F 1 duplex structures during D2. Out-of-sequence D3 fault systems, truncate the antiformal culmination and incorporate slices of volcanic rocks in an east- verging imbricate fan, and locally form discreet melange zones. D4 consists of a steep northerly-striking fault system with apparent sinistral strike-slip fault displacements. The complex structural systems mapped in this area demonstrate that careful, detailed

tectono-stratigraphic studies are required to resolve the tectonic history of the allochthon and emplacement mechanisms of the Bay of Islands Ophiolite Complex.

Acknowledgments

I would like to thank my supervisors, Drs. T. Calon and E. Burden for providing both a research project and financial assistance through their grant. Their advice, encouragement, and willingness to share knowledge allowed me to grow in leaps and bounds as a geologist.

This project was supported by the Earth Sciences Sector of Natural Resources Canada through a contribution to Memorial University under the Canadian Geosciences National Mapping Program Appalachian Forelands and Platform architecture project.

This support was used to complete field work in the Bay of Islands and provided analysis of palynology samples. I thank Denis Lavoie for his commitment and interest during the span of the project. Through Denis Lavoie the project was provided logistical and equipment support from the Geological Survey of Canada.

Jennifer Young, Melissa Putt, and Allison Cocker worked with me as field assistants during two summer field seasons. I thank them for the tenacity during the often brutal stream and tuck-a-more traverses in the Frenchman's Cove area. Their ability and ideas as geologists were great contributions to the project and I learned a lot about Newfoundland through them.

Mark Childs, Marlaine and Junior Childs, Jerry and Rose Sheppard, and Glen Pennel provided logistical support throughout the project. The hospitality of these generous individuals and their families made our field crews feel welcome in their communities. The quality of seamanship demonstrated by Jerry Sheppard and Glen

Pennel allowed us access to the coastal sections that would have otherwise been unavailable.

Peer support was always available to me at Memorial University. Vanessa Bennett and Don Wright provided scientific, educational, and personal support. Dr. J.

Waldron, Amber Henry, and James Bradley of the University of Alberta provided many helpful discussions during field work. Exposure to their field area, ideas, and expertise on the geology of the Humber Zone was a great benefit to myself and helped to develop my knowledge of the Humber Arm Allochthon.

Finally I thank my wife, Debra Buchanan, for her fortitude, patience,, and support.

Without her I could not have finished this thesis. We knew it would be a crazy time in Newfoundland and it was. If we can m~age this, then we can manage anything.

Table of Contents

Abstract ... ii

Acknowledgments ... iv

Table of Contents ... vi

List ofFigures ... ix

List of tables ... xii

Chapter one: Introduction ... 1

1.0 Introduction ... 1

1.1 Study area and location ... 2

1.2 Regional geology of the external Humber Zone ... 6

1.2.1 Geology of the autochthon ... 6

1.2.2 Geology of the Humber Arm Allochthon in Bay of Islands ... 8

1.3 Purpose and scope of the project ... 9

1.4 Methodology ... 11

Chapter two: Evolution of geological thoughts on the Humber Arm Allochthon ... 13

2.1 Previous work in the Frenchman's Cove- York Harbour area ... 13

2.2 Emplacement mechanisms for the Bay of Islands Ophiolite Complex ... 21

2.3 Melange development ... 24

Chapter three: Lithostratigraphy ... 28

3.1 Lithostratigraphy of the Frenchman's Cove- York Harbour area ... 30

3 .1.1 Blow Me Down Brook formation ... 30

3.1.2 Irishtown formation ... 31

3.1.3 Cook's Brook formation ... : ... 33

3.1.4 Middle Arm Point formation ... 34

3.1.5 Eagle Island formation ... 36

3.1.6 Wood's Island and Frenchman's Cove volcanics ... 38

3.2 Paleontology and Palynology occurrences in study area ... 41

3.2.1 Oldhamia Occurrences ... 43

3 .2.2 Palynology of strata of the Humber Ann Allochthon ... 44

3.2.3 Thermal alteration patterns from processed palynology samples ... 48

Chapter four: Tectono-stratigraphic domains ... 51

4.1 Domain 1 ...•...•...•...•.•...•.... 52

4.2 Domain 2 ... 53

4.3 Domain 3 ...•.•...•...•..•... 55

4.4 Domain 4 ...•.•..•...•...•... 56

4.5 Domain 5 ...•...•..••....•...•.•... 57

Chapter five: Fold systems ... ⁿ • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 60 5.1 F ¹ fold system ... 60

5.2 F ² fold systems ...••.•...•... 65

5.2.1 Domain 1 ... : ... 65

5.2.2 Domain 2 ... 69

5.2.3 Domain 3 ... 74

5.2.4 Domain 4 ... 78

5.2.5 Domain 5 ... 82

5.3 F 3 fold systems ···~··· 90

5.4 Interference patterns formed by superposition of fold generations ... 94

Chapter six: Cleavage development ... 103

6.1 St cleavage ... 1 03 6.2 S2 Cleavage ...•...•...•...•...•...•.•... 108

6.3 Cleavage development in the Blow Me Down Brook formation ... 111

Chapter seven: Fault systems ...... 112

7.1 F ¹ thrust faults ...•..•...•...•...•...•...•... 113

7.1.1 Domains 1, 2, and 5 ... 113

7 .1.2 Shear zone at boundary of Domains 4 and 5 ... 115

7.2 F 2 thrust faults ...•...•.•... 118

7 .2.1 Domains 1 and 5 ... 118

7.2.2 Domain 2 ... 119

7.2.3 Domain 3 ... 121

7.2.4 Domain4 ... 125

7.2.5 Domain 5 ... 127

7.3 F 3 thrust system ... 130

7.3.1 West of Frenchman's Cove ... 131

7.3.2 Wood's Island ... 133

7.3.3 South of Frenchman's Cove ... 134

7.5 Post F 3 faults ... 138

7.6 Melange in the Frenchman's Cove-York Harbour area ... 141

Chapter eight: Sequence and timing of structural events in the Frenchman's Cove - York Harbour area ... 146

8.1 Determination of regional deformation events ... 146

8.2 Phases of deformation ... 152

8.2.1 D1 deformation ... 152

8.2.2 Dz deformation ... 157

8.2.3 D3 deformation ... 162

8.2.4 D4 deformation ... 165

8.3 Melange vs. dismemberment and mixing during polyphase deformation .... 167

8.4 Proposed tectonic setting ... 172

8.5 Conclusions ... 17 4 References cited ... 179

Appendix A- Sample lists ... 188

Appendix B - Field stations ... .-... 201

Appendix C- Geochemistry analysis ... 215 Insert I Geology of the Frenchman's Cove- York Harbour area, Bay of Islands, Newfoundland ... pocket Insert II Cross-sections for Domains 1, 2, and 3 ... pocket Insert III Cross-sections for Domains 4 and 5 ... pocket Insert IV Locations of Field Stations ... pocket

List of Figures

Figure 1.1 Major lithotectonic zones ofNewfoundland (after Williams, 1973) and the

lithotectonic components of the Humber Zone (after Waldron and Stockmal, 1994) .... 3

Figure 1.2 Regional geology in the vicinity of the study area from Williams and Cawood ( 1989) .•..•...••..•.••....••...•...•••...•...•...•...•...••..••..•••...•... 5

Figure 2.1 Development of stratigraphy in western Newfoundland and the Bay of Islan.ds (after Botsford, 1988) ...•....••...•.•..•...••....•....•••..•..•.••..•....••.•....•••••...•..•...••..• 17

Figure 2.2 Regional cross-section through the Little Port Complex, Blow Me Down Ophiolite Massif, and the western limb of the Cook's Brook Syncline (from Williams an.d Cawood, 1989) ...•...•.••.••.•.•..••••.•.•..•••...•...•••..•.••.•.••...•..•..•.••••..••.•••.•...•... 18

Figure 2.3 Raymond's (1984) classification for melanges. This chart divides the continuum of dismemberment into four stages with sub-divisions based on tectonic origin .•...•..••...•..••....•...•..•...•.•..••..•..•••....••...•....•.••..•...•....•...•...••..•.••..•...•...•. 26

Figure 3.1 Lithostratigraphic chart of the sedimentary rocks in the Humber Arm Allochthon. After Botsford (1988). See also Figure 2.1 for tectono-stratigraphic relationships .•••.•.••.••.••.••.•...•..••....•.•••••.•.•.•...•.•••..••..•••...••••••.•••••.•••••..•...•..••••••.•....•..•..•..• 29

Figure 3.2 Lithological sections of the Blow Me Down Brook formation. Arrow indicates yormging direction of th.e beds ....••...•.•..••.•.••....••••.••..••..•...••...•..••...•.•... 32

Figure 3.3 Lithological sections of the Cook's Brook formation. Arrow indicates younging direction of the beds .•...•••.•••..•.••..•..•...••....•...•..•••.•..••...••..••.••..•.••...••.•...•.. 35

Figure 3.4 Typical lithologies of the Middle Arm Point formation ... 37

Figure 3.5 Lithological sections of the Eagle Island formation. Arrows indicate yormging direction of the beds .••.••••...•....••.•.•••...•.•...•...•.•••...•...•.••.•••••.••.••...•..•..• 39

Figure 3.6 Rock type and tectonic setting discrimination plots using trace elements. 42 Figure 3. 7 Location of samples processed for palynology in study area ... 45

Figure 5.1 Common morphological expression ofF ₁ folds in Domains 1 and 2 ... 62

Figure 5.2 Morphological expressions ofF ₁ folds in Domain 3 ... 64

Figure 5.3 Morphological expressions of F2 folds in Domain 1. ... 67

Figure 5.4 Lower hemisphere, equal area projections for orientation data defining the F 2 fold-thrust system in Domain 1 ..•..•••...•••••.••••...•.•.••...••...•..•.•.••.•...•.•...•••....•.••..• 68

Figure 5.5 Morphological expressions of F₂ folds in Domain 2 ... 70

Figure 5.6 Lower hemisphere, equal area projections for orientation data defining the F2 fold-thrust system in Domain 2 (Insert II, sections E-E', F-F', and G-G'-G") ... 72

Figure 5.7 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 2b (Insert II, Section H-H') ...•...•...•... 73 Figure 5.8 Gently east-plunging F2 fold in thick-bedded sandstones within Domain 3b (Insert IV, station 11001) ...•...•...•.•..••..•...•...••.•.•.••.•.••.•••..•.... 75 Figure 5.9 Lower hemisphere, equal area projections for orientation data defining the F2 fold-thrust system in Domain 3b (Insert II, Section K-K') ... 77 Figure 5.10 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 3c (Insert II, Section L-L') ... 79 Figure 5.11 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 4, on Wood's Island and Seal Island (Insert III, sections M-M' and N-N') ...•••.•....•.•.•..•...•...•... 81 Figure 5.12 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 5 (Insert III, Section 0-0') ...•.•...••.•.•... 84 Figure 5.13 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 5 (Insert III, sections P-P' and Q-Q') .•.••...•••... 85 Figure 5.14 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 5 (Insert III, sections R-R'-R" and S-S') ...•... 87 Figure 5.15 Recumbent F2 fold related to a southwest-verging backthrust in the F2

fold-thrust system in Domain 5 (Insert III, Section S-S') ... 89 Figure 5.16 Lower hemisphere, equal area projections for orientation data defining the Fz fold-thrust system in Domain 5 (Insert III, Section T-T'-T") ..•...•..•... 91 Figure 5.17 A broken F3 fault-propagation fold in a sandstone succession of the Blow Me Down Brook formation (Insert II, Section I-1') ....••...••...••.•.•...•.•..•...••• 93 Figure 5.18 Lower hemisphere, equal area projections for orientation data defining the F3 fold-thrust system in Domain 3c (Insert II, sections I-I' and J-1') .•••••••••••••••••••••• 95 Figure 5.19 Spectrum of interference patterns developed by the superposition of fold systems with different orientations (from Ramsay and Huber, 1987) ... 97 Figure 5.20 Examples of the dominant fold interference patterns developed by the superposition ofF 1 and F 2 fold systems in the map area ... 99 Figure 5.21 Possible asymmetries of mushroom-type structures, depending on the trend of the F1 fold system at the time ofF2 superposition ...•... 101 Figure 6.1 F 1 folds demonstrating cleavage fanning around the hinge due to the

development of longitudinal strain fields in the competent limestone beds (Insert III, Section R-R') ........ 106 Figure 7.1 F1 shear zone at the base of the Wood's Island Volcanics and the associated kinematic indicators (Insert III, Section N-N', Detail B) ... 116

Figure 7.2 Style ofF2 thrust faults in Domain 3 . ... 122 Figure 7.3 Stereoplots presenting fault plane and fault kinematic data for the late, northerly striking fault population, which overprints the area . ... 124 Figure 7.4 Kinematic indicators developed in the brittle-ductile fault zone at the top of the Wood's Island Volcanics. Arrows depict the shear sense . ...•... 135 Figure 7.5 An east-verging F3 thrust fault separating listwanite in the hanging wall from dismembered shale and sandstone in the footwall (Insert I, station 486) ..••... 136 Figure 7.6 Stereoplots presenting fault plane and fault kinematic data for the late, northerly striking fault population, which overprints the area . ... 140 Figure 7.7 Fabrics and exotic blocks of mixed lithologie set in a strongly cleaved shale matrix in the melange zone on Wood's Island (Insert III, Section T'-T") . ... 144 Figure 8.1 Schematic sections depicting the evolution of broken, recumbent F 1 folds, which develop nappe-type structures. The brittle-ductile style of deformation is the result of progressive loading during the emplacement of the Blow Me Down Brook formation and Blow Me Down Ophiolite massif in the D₁ deformation event (not to scale) ... 155 Figure 8.2 Schematic sections depic_ting the evolution of the F 2 anti formal

culmination in D2. Note the high density ofF2 thrust faults and accommodation faults in the core of the culmination, which re-imbricate the folded F 1 duplex structures (not to scale). Detailed, accurate cross-sections are presented on Insert II, sections A to H.

General form of the Cook's Brook syncline is adapted from other workers (Stevens, 1965; Waldron et al., 2003) ...•...•... 160 Figure 8.3 Schematic sections depicting the out-of-sequence F3 fold-thrust system truncating the F2 antiformal culmination during D3. The F3 faults inherit the volcanic rocks by re-imbricating D₁ duplex structures, which are re-folded by the F2 fold system (not to scale). See Insert II, section I to J and Insert III, Section N-N', Detail C for accurate and detailed sections of the F 3 fold-thrust system. General form of the Cook's Brook syncline is adapted from other workers (Stevens, 1965; Waldron, et al., 2003) . ... 164

List of tables

Table 3.1 Summary of palynology results correlated to each formation of the Humber Arm Supergroup in the study area ... 4 7

Chapter one:

Introduction

1.0 Introduction

Western Newfoundland has been of interest to geologists for over one hundred years. Some of the earliest investigations of the rocks in this region were completed by Logan (1863), helping to form his ideas about the geology of eastern Canada. The deformed rocks of eastern Canada and Newfoundland were recognized by Logan (1863) to be a part of the Appalachian Mountains of the southeastern United States. During this early time the distribution of igneous, continental and marine sedimentary rocks and their deformation patterns in orogenic belts were modelled as geosynclines (Kay, 1951 ).

Geosyncline theories do not provide an adequate mechanism to account for the kinematics and styles of orogenic deformation, although, the models remained popular for almost a century (Reading, 1986).

In the second half of the twentieth century the rocks of western Newfoundland provided significant evidence in support of plate tectonic theory. The recognition that the

Newfoundland Appalachians contained all the components of a complete Wilson Cycle (Wilson, 1966) revolutionized geological understanding of the Appalachian Orogenic Belt. Oceanic spreading and subduction processes of plate tectonic theory provide deformation mechanisms which account for orogenic belts along plate margins and the presence of oceanic lithosphere in these belts (Bird and Dewey, 1970; Church and Stevens, 1971; Dewey and Kidd, 1974). Williams (1964 and 1979) established four northeasterly trending lithotectonic belts on the island of Newfoundland, each distinguished by characteristic stratigraphic, petrologic, and structural elements (Figure 1.1). Together the Humber, Dunnage, Gander, and Avalon zones represent the development of a stable, Laurentian continental margin, growth and collapse of the Iapetus Ocean, accretion of an exotic terrane and ultimately the docking of an outboard continental plate. These processes occurred during three phases of deformation: the Taconic, Acadian, and Alleghanian orogenies.

The Humber Zone contains the remnants of the Laurentian margin. The Hare Bay and Humber Arm allochthons preserve the distal components of the margin, providing structural windows into the architecture of the margin. The complex internal structure of the Humber Arm Allochthon contains the history of the Laurentian margin. Careful, detailed geological studies can unravel this history and describe the tectonic processes which formed western Newfoundland

1.1 Study area and location

The study area is located on the west coast of Newfoundland forty kilometres west of Comer Brook (Humber Arm 12 G\01 NTS sheet). The southern boundary of the

(1 :3 377 372)

Legend

Carbonate Platform Rocks Allochthonous Rocks

• Ophiolite Complexes

D Grenville age basement _ _ _ Boundary of the external and

internal Humber Zone

~ Hare Bay Allochthon

Gander River Ultramafic Belt

N

Figure 1.1 Major lithotectonic zones ofNewfoundland (after Williams, 1973) and the lithotectonic components of the Humber Zone (after Waldron and Stockmal, 1994)

study area follows the northern edge of the Blow Me Down Ophiolite Massif (Figurel.2). The area also includes Governor's Island, Seal Island, and the southern shoreline ofWood's Island.

Access to the area is provided by Highway #450 on the southern shore of Humber Arm and Bay of Islands. Shoreline traverses can be started at several locations, where side roads lead to beach cabins. Boats are necessary for access to the islands and several coastal locations where sea cliffs prevent shoreline access. Submerged boulders, reefs, and rocky shorelines limit landing points and these traverses are best undertaken at low tide and when the wind is down. Experienced boatmen and dories can be hired in the communities of Frenchman's Cove, York Harbour, and Lark Harbour.

The terrane is rugged and traverses away from shoreline exposures are difficult.

Vegetation covers 100% of the area, ranging from grass meadows and bog at higher elevations to tuckamore and thick second growth forest at lower elevations. In thickly vegetated areas outcrop is limited to streambeds and cliff faces on the higher hills. At York Harbour the Brooms Bottom Lowlands, a wet bog, extends south to the Serpentine River between Blow Me Down Mountain and Virgin Hills. Scree and boulder fields shed from the ophiolite massif, cover bedrock close to the massif.

Sea cliffs provide the best exposure of the deformed sedimentary rocks. Eighty to ninety percent of the twenty-seven kilometres of shoreline has exposed cliff faces and occasional wave cut platforms. Unfortunately, many of the three-dimensional relationships of the structural geology in this area are only partially displayed by largely two-dimensional exposures. Relief of the sea cliffs is generally limited to between ten

N

COLv - BAY

OF CSU.. DS

Geology Legend (from Williams and Cawood, 1989)

COL Little Port Island Arc Complex COFI Fox Island River Group

COB Blow Me Down and Lewis Hills ophiolite massifs Om Melange

Ommc "Companion Melange"

Humber Arm Supergroup

HCBB Blow Me Down Brook formation HCs Summerside formation

CI Irishtown formation

CO Platform sequence - undivided COcb Cook's Brook formation OMA Middle Arm Point formation OEI Eagle Island formation

Figure 1.2 Regional geology in the vicinity of the study area from Williams and Cawood (1989).

and twenty metres and rarely exceeds thirty metres, the elevation of a regionally prominent glacial terrace bordering much of the coast line.

1.2 Regional geology of the external Humber Zone

The Humber Zone (Figure 1.1) is the western lithotectonic zone of the Newfoundland Appalachians (Williams, 1979). It is characterized by two allochthonous terranes, capped by ophiolite and igneous complexes and emplaced onto the autochthonous carbonate platform during telescoping of the Laurentian margin (Figure 1.1 ). The western boundary of the Humber Zone is coincident with the western limit of Appalachian deformation. The intensity of deformation and metamorphism increases to the east across the zone and forms the external and internal subzones (Williams, 1975).

Structural styles also change in response to the metamorphic gradient, gradually becoming more ductile. A prominent cleavage fan in the eastern portions of the allochthon is a notable feature formed because of the increasing metamorphic grade (Williams, 1975; Waldron et. al., 1998). These gradual changes in deformation regimes across a narrow belt reflect the complex deformation history of the Humber Zone during both the Taconic and subsequent orogenic events (Williams, 1975; Cawood and Botsford, 1991).

1.2.1 Geology of the autochthon

The lowest stratigraphic sequences of the autochthon are the clastic successions of the Precambrian to Middle Cambrian Labrador Group, which are deposited nonconformably on Grenville age basement of the Laurentian Margin (Williams and

Stevens, 1974; Cawood Nemchin, 2001; Waldron et al., 1998). Volcanic flows that overlie and cut these sedimentary successions have been dated at 550 Ma (Bostock et al., 1983; Krogh, 1982; McCausland et al., 1997), and suggest that initial rifting of the Laurentian margin occurred between 570 Ma and 550 Ma (McCausland and Hodych, 1998). The transition from active rifting to oceanic spreading occurred in the middle Cambrian and is marked by the stratigraphic transition from shallow water clastic sedimentary rocks to deep water shale facies of the rift fill sedimentary rocks (Williams and Hiscott, 1987; Lavoie et al., 2003). Development of an expansive, stable continental margin during a phase of oceanic spreading represents a relatively quiescent tectonic period.

The Middle Cambrian carbonate platform conformably overlies Early Cambrian rocks of the Labrador Group (Williams and Stevens, 1974). In Newfoundland the carbonate platform is subdivided into the Middle to Upper Cambrian Port au Port Group, Upper Cambrian to Lower Ordovician St. George Group, and the Middle Ordovician Table Head Formation (Waldron et. al., 1998). The presence of algal mounds, desiccation cracks, and local erosional-disconformities indicates that the platform formed in a shallow water carbonate environment (James et al., 1987). A significant erosional disconformity is present between the Lower Ordovician St. George Group and the Middle Ordovician Table Head Formation (Williams and Stevens, 1974; Waldron et al., 1998).

This disconformity is widespread across the autochthon, but is not distinguished in the deeper water continental slope facies preserved in the allochthons.

1.2.2 Geology of the Humber Arm Allochthon in Bay of Islands

Located in the external Humber Zone, the Humber Arm Allochthon is a strongly deformed, but largely unmetamorphosed, terrane of sedimentary and igneous rocks (Williams, 1973; Williams, 1975). The Bay of Islands provides a classic cross-section through the allochthon and frontal portion of the Appalachian Orogenic Belt, demonstrating the telescoping of oceanic crust, outer shelf and slope sedimentary rocks, and tectonic emplacement onto the shallow-water carbonate platform of the autochthon (Williams and Stevens, 1974; Williams and Cawood, 1989).

The allochthon contains four major thrust slices comprised of the Humber Arm Supergroup (Figure 1.2) and the Bay of Islands Ophiolite and Little Port complexes (Williams, 1973; Williams and Cawood, 1989). The lower slices contain the distal margin rocks of the lower to middle Cambrian Curling Group and the middle Cambrian to Tremadoc Northern Head Group. Isolated within the intermediate slice is the coarse, rift-related sandstone of the lower Cambrian Blow Me Down Brook formation. The Arenig-Llanvirn Eagle Island formation, a syntectonic flysch, is found at several structural levels of the allochthon. Igneous rocks of the Bay of Islands Ophiolite and Little Port complexes form the uppermost structural slices, lying as klippen on the sedimentary rocks of the Humber Arm Allochthon.

Structural boundaries between successive slices of the allochthon have been mapped as tectonic melange by previous workers (e.g., Stevens, 1970; Williams and Godfrey, 1980; Waldron, 1985; Williams and Cawood, 1989; Waldron et al., 1998).

Polyphase folds, penetrative cleavage, and exotic blocks in these belts form strong

structural fabrics with a chaotic appearance. The "Companion Melange" at Frenchman's Cove (Figure 1.2) is considered to be a critical exposure of melange at the contact between the igneous and sedimentary slices of the allochthon.

1.3 Purpose and scope of the project

Previous work in the Humber Arm Allochthon has focused on resolving the stratigraphy and structure of the Humber Arm Supergroup in the northern and eastern portions of the allochthon. Although the Blow Me Down Brook formation has been the subject of stratigraphic studies (e.g., Stevens, 1965; Quinn, 1988; Palmer et al., 2001), the allochthonous sedimentary rocks in the western portions of Bay of Islands have received little detailed research into their structural and stratigraphic architecture.

The southern shoreline of the Bay of Islands from Frenchman's Cove to York Harbour provides exposure through a steep, poly-deformed structural belt at the contact between the upper and intermediate slices of the allochthon. Within this belt, the sedimentary rocks of the Humber Arm Supergroup are overprinted by successive fold generations, related fabrics, and faults.

The main purpose of this thesis is to provide a detailed analysis of the structural architecture and deformation history in this portion of the allochthon. In light of the re- assignment of the Blow Me Down Brook formation to the Early Cambrian (e.g., Lindholm and Casey, 1989), lithostratigraphic aspects of the allochthon were re-visited in this area. Palynology samples were collected to provide new biostratigraphic data in an attempt to refine the age and stratigraphic position of stratigraphic units in the allochthon, particularly the Blow Me Down Brook formation. Previously many of the rocks in the

Frenchman's Cove - York Harbour area were assigned to melange. However, the presence of coherent stratigraphic successions contained in fine-scale structural domains allows these rocks to be correlated with the stratigraphy of the allochthon.

A comprehensive set of structural data was collected across the boundaries of the belt. The data depicts the nature and geometry of the boundaries and structural systems developed during the emplacement and deformation of the allochthon. Detailed maps and cross-sections (Inserts I, II, and III) were compiled from continuous logs of the shoreline and delineate distinct domains of unique stratigraphy and structural relationships. The stratigraphic-structural architecture indicates that four phases of deformation have affected the Humber Arm Allochthon. The diverse nature of the documented fold\fault systems further challenges current models that this highly deformed belt is a melange developed in a horizontal shear zone at the base of the Bay of Islands Ophiolite Complex (e.g., Williams, 1975; Waldron, 1985; Wojtal, 2001).

The tectono-stratigraphic domains are a core component of this thesis and the organization of this thesis reflects the significance of the domains. Chapter two is a review of previous work in the Frenchman's Cove area, emplacement mechanisms for the Bay of Islands Ophiolite Complex, and aspects of melange formation. Descriptions of the lithostratigraphic units utilized to develop the structural architecture and the results of preliminary palynology studies are presented in Chapter three. An overview and descriptions of the tectono-stratigraphic domains is presented in Chapter four. Chapters' five to seven present the structural data and detailed descriptions of individual structural systems in each of the domains. Chapter eight considers the structural architecture and

deformation history developed in this thesis and its implication to current geological models of the Humber Arm Allochthon and the formation of melange.

1.4 Methodology

The data collection for this thesis utilized standard geological field techniques.

Orientation data was collected using a Freiburg fabric compass and was recorded in field books using dip\dip-direction convention. However, planar structural data is presented in the thesis using the right-hand rule (e.g., strike\dip RH- 120\45 RH)). Coastal exposures were mapped by sketching a series of continuous strip-sections of the exposed sea cliffs.

The sketches are anchored approximately every fifty metres using a Garmin GPS unit.

Outcrop discovered during inland traverses was located using a Garmin GPS unit and then plotted onto a regional base map using Maplnfo. All collected GPS stations, structural measurements, and collected samples were entered in a Microsoft Access database.

Maplnfo was used to manipulate data in the Access database and compile the fmal geological map (Insert I). The cross-sections (Inserts I and II) were constructed using standard structural techniques. Lower hemisphere, equal area plots of orientation data were used to analyse the geometry of the fold systems mapped in each of the structural domains. The stereographic plotting was completed using a program called GEOrient. The cross-sections are oriented perpendicular to the trend of the second generation fold-thrust systems, except in Section N-N' (Insert II), this section is an up- plunge profile of the large anticline on Wood's Island. Although fold profiles are typically constructed as down-plunge views, an up-plunge view was chosen for this

profile in order to present the geometry of the fold in the same orientation as it is viewed along the shoreline outcrop (i.e., looking north). GEOcalculator was used to convert the orientation of measured planar features (e.g., bedding, cleavage, faults, and axial surfaces) to pitches on the plane of each cross-section or fold profile. Cross-sections were chosen over fold profile sections, because the cross-sections are more visually representative of cliff exposures present in the map area. Because the F2 folds systems are generally gently plunging the error in bed-thickness and angular relationships is not that large. Furthermore, the strong dismemberment and imbrication of the stratigraphic successions in the eastern portions of the map area limits the degree to which the fold systems can be reconstructed. Standard fold reconstruction techniques are used where it is possible to constrain the geometry of individual folds or fold trains with detailed bedding and cleavage measurements. . The most notable use of these techniques are presented on Insert II, sections I to J and Insert III, Section N-N' where the extensive sections were reconstructed using Kink method techniques (Marshak and Mitra, 1988).

The textbook, titled "Basic methods of structural geology" by Marshak and Mitra (1988), presents detailed treatments of cross-section construction, fold reconstruction techniques, and techniques and methods used to analyse and manipulate orientation data on lower hemisphere, equal area plots. GEOrient and GEOcalculator are shareware programs written by Dr. R.H. Holcombe at the Department of Earth Science, The University of Queensland.

Chapter two:

Evolution of geological thoughts on the Humber Arm Allochthon

2.1 Previous work in the Frenchman's Cove- York Harbour area

The first geological surveys of western Newfoundland were broad, regional studies encompassing large areas and focusing primarily on traverses of the extensive coastal exposures. Murray and Howley (1881) and Howley (1907) produced the earliest geological maps of western Newfoundland, correlating the abundant shale and sandstone successions with the Silurian successions in Quebec.

Schuchert and Dunbar (1934) undertook an extensive geological survey of western Newfoundland in the 1920s. Based on lithology and fossil assemblages Schuchert and Dunbar (1934) grouped the shale, sandstone and carbonate sequences into seven series (Figure 2.1A). At Curling; a graptolite occurrence constrains the top of their stratigraphic succession, the Humber Arm Series (Figure 2.1A), to the Middle Ordovician. Schuchert and Dunbar's (1934) stratigraphy was a marked departure from

earlier correlations with Silurian sedimentary rocks in Quebec (Logan, 1863; Murray and Howley, 1881; Howley, 1907)

Applying the models of geosyncline development, Schuchert and Dunbar (1934) described the geological evolution of western Newfoundland as an elongate geosyclinal trough. They identified three periods of deformation related to tectonic upheaval and igneous intrusions. In the Bay of Islands Schuchert and Dunbar (1934) considered the igneous complex to be the result of middle Ordovician intrusive activity culminating with the intrusion of Devonian gabbro laccoliths. Intense folding and faulting observed in the Humber Arm Series was attributed to intrusion of the laccoliths (Schuchert and Dunbar, 1934).

Cooper (1936) and Smith (1958) recognized that the igneous rocks were over- thrust on the sedimentary rocks, but still considered the complex to have a local plutonic origin associated with volcanic rocks of region. Amphibolite grade metamorphic rocks were considered a basal aureole imprinted on the surrounding sedimentary rocks during emplacement of the complex (Cooper, 1936; Smith, 1958; Williams, 1971). Cooper (1936) named the suite of igneous rocks the Bay of Islands Igneous Complex

A series of investigations by Walthier (1949), Weitz (1953), and Lilly (1963) attempted to develop the regional stratigraphy, but due to the localized nature of the studies their stratigraphic divisions did not easily extrapolate beyond the study areas.

Kindle and Whittington (1958) collected extensive graptolite and trilobite assemblages along the coast and constructed a depositional time frame ranging in age from the late Cambrian to middle Ordovician. Kindle and Whittington (1958) also described the

depositional environments of the sedimentary successions, relating them to the deep water edge of the western carbonate platform identified by Johnson (1941) and Kay (1945; 1951).

In a then revolutionary paper, Rodgers and Neale (1963) suggested that all of the allochthonous deep-water sedimentary rocks were emplaced, from the east, onto an autochthonous carbonate platform, similar to the klippe in the Taconic region of New York. This model of westerly transported terranes became the basic component for all later tectonic models in western Newfoundland (Stevens, 1965; Bruckner, 1966; Lilly, 1967; Williams, 1975). The allochthons of Rodgers and Neale (1963) consisted of the sedimentary rocks mapped by Schuchert and Dunbar (1934) as the Humber Arm Series, the Cow Head Breccia, and the Bay of Islands Igneous Complex.

The advent of the theories of continental drift, plate tectonics (Dewey, 1969) and oceanic cycles (Wilson, 1966) in the 1960's had a profound impact on the geological understanding of western Newfoundland. Plate tectonics allowed the synthesis of the Humber Zone geology into a holistic model involving a progression of tectonic settings.

Departing from the igneous intrusion models of Cooper (1936) and Smith (1958), the Bay of Islands Igneous Complex was recognized as a remnant of oceanic lithosphere (Stevens, 1970; Dewey and Bird, 1971), a fundamental leap in the understanding of the geological evolution of western Newfoundland.

Stevens (1970) formalized the stratigraphy of the allochthon as the Humber Arm Supergroup containing the Cow Head and Curling groups. In the Humber Arm region, the Curling Group was subdivided into three flysch units derived from the carbonate

platform to the west, and from the advancing Taconic thrust sheets in the east (Figure 2.1D). Stevens (1970) included Bruckner's (1966) stratigraphy of the allochthon as informal formational units of the Curling Group. This informal stratigraphy is commonly used in current literature and includes the following formations: the Irishtown (Stevens, 1965), Summerside (Stevens, 1965), Cook's Brook (Stevens, 1965), Middle Arm Point (Stevens, 1965), and Blow Me Down Brook (Lilly, 1967). The Bay of Islands Ophiolite Complex was, for the first time, considered to be a far travelled thrust slice emplaced at the highest structural level of the Allochthon (Stevens, 1970).

Strongly deformed sedimentary rocks in Frenchman's Cove, previously mapped as chaotic zones, were interpreted as tectonic melange at the contact of successive structural slices of the allochthon (Stevens, 1970). Each of the structural slices was bound by melange formed during the transportation and assembly of the allochthon (Stevens, 1970; Williams, 1973). Regional mapping by Williams (1973), Comeau (1972), Schillereff and Williams (1979), Godfrey (1982) and Williams and Cawood (1989) delineated a broad belt of strongly deformed sedimentary rocks of the Curling Group. Rare "knockers" of volcanic and ultramafic rocks, mostly in close proximity to the ophiolite massifs, were used to define the complex belt as tectonic melange (Williams and Godfrey, 1980; Williams and Cawood, 1989). The melange was considered to be the tectonic contact between the Bay of Islands Ophiolite Complex and lower slices of the allochthon (Williams and Godfrey, 1980; Waldron, 1985; Williams and Cawood, 1989).

The position of melange at the boundaries of each thrust sheet is illustrated in Figure 2.2, a regional cross-section produced by Williams and Cawood (1989). The section

Stevn~ 1965 Bruckner, 1966 Stevtn~ 1970 Period

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Figure 2.1 Development of stratigraphy in western Newfoundland and the Bay oflslands (after Botsford, 1988).

BoMord,l9!8

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E

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Figure 2.2. Regional cross-section through the Little Port Complex, Blow Me Down Ophiolite Massif, and the western limb of the Cook's Brook Syncline.

Location of Section G-G' is shown on Figure 1.2 (from Williams and Cawood, 1989)

~

\) G'

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depicts sub-horizontal structural contacts between the Blow Me Down Brook Ophiolite Massif, melange, and the lower, sedimentary slices of allochthon. In this configuration the ophiolite massifs must lie as klippen in the uppermost levels of the allochthon.

At Frenchman's Cove the "Companion Melange" is an extensive belt of dismembered and polyphase deformed sedimentary rocks of the Humber Arm Supergroup, considered to be the best exposure of melange in the area (Stevens, 1970;

Williams, 1973; Williams, 1975; Waldron, 1985). Criteria used to identify melange include shale injection, quartz filled tension gashes perpendicular to bedding, isolated fold hinges, scaly cleavage, and broken formation (Waldron, 1985). Bosworth (1984) introduced the concept of structural slicing to account for the development of rhomboidal, lens-shaped blocks during dismemberment of the stratigraphic succession.

Structural slicing produces small-scale fault systems with the same geometry as larger scale thrust systems, progressively dismembering coherent bedding. Bosworth (1984) interpreted the development of melange at Frenchman's Cove as the result of overprinting of first generation folds by a slaty cleavage associated with the development of later, second generation, east-verging folds and thrusts. Waldron (1985) also identified two generations of folds in the eastern portion of the Humber Arm, but does not discuss the implications of second generation asymmetry. Waldron et al. (1988) relates the formation of melange to the olistostromal style slumping of poorly lithified and water-saturated sedimentary rocks of an over steepened accretionary wedge. In contrast, Wojtal (2001) interpreted fault arrays in the melange to have developed during

thrusting in a general non-coaxial shear environment. The orientation of the fault arrays are similar to the development of conjugate Riedel shears and indicate northwest-verging shear, consistent with regional shortening in the Bay of Islands (y./ojtal, 2001).

Botsford (1988) completed a detailed stratigraphic study of the carbonate flysch units in Steven's (1970) Curling Group, but this nomenclature has never been formalized in literature. Using graptolite assemblages Botsford (1988) restricted the siliciclastic Summerside and Irishtown formations to the early Cambrian Curling Group and separated the calcareous Cook's Brook and Middle Arm Point formations into the new, middle Cambrian to early Ordovician Northern Head Group (Figure 2.1). Occurrences of the Arenig graptolite Isograptus victoriae victoriae marked the upper boundary of the Middle Arm Point formation and established the depositional age of the Eagle Island formation, a siliciclastic Ordovician flysch unit. Lindholm and Casey (1989) discovered the Cambrian trace fossil Oldhamia in the shale components of the Blow Me Down Brook formation. This made it possible to separate coarse sandstone units of the Blow Me Down Brook formation from the Arenig Eagle Island formation. The revisions to the depositional age of the formations are reflected in the work of Williams and Cawood (1989). However, this map compilation does not consider the impact of these new ages to the regional distribution of each .formation or the structural architecture of the allochthon.

Quinn (1992) compared occurrences of Ordovician flysch units across the Humber Arm Allochthon and described in detail the sedimentology of the Lower Head Formation and Goose Tickle Group. In this study Botsford's (1988) Eagle Island

formation was considered to be part of the Lower Head Formation (Quinn, 1992). Quinn (1995) proposed a depositional model based on the input of syntectonic sediment input via submarine canyons. The large number of sub-environments in this model accounts for the lithological diversity observed in each of the Ordovician flysch units (Quinn, 1995).

Recent mapping initiatives in the Bay of Islands area have focused on resolving the stratigraphy, regional distribution, and the structural architecture of the Humber Arm Supergroup. In the eastern portions of the allochthon Palmer et al. (200 1) completed detailed surveys and measured several stratigraphic sections of the Curling Group and Blow Me Down Brook formation in an attempt to define type sections for these stratigraphic packages. The nature of deformation in the area limits the available exposures of the units and it was not possible to establish type sections (Palmer et al., 2001). Based on this mapping, Waldron et al. (2002) identified north-south striking belts formed by an imbricate stack of the Humber Arm Supergroup. In the western extent of the allochthon Burden et al. (200 1) and Calon et al. (2002) demonstrated that melange in the vicinity of the Little Port Complex can be subdivided into mappable stratigraphic units. The regional distribution and extent of these units indicate that it is possible to resolve the complex internal structure of the Humber Arm Supergroup and the allochthon.

2.2 Emplacement mechanisms for the Bay of Islands Ophiolite Complex

Ophiolite complexes in the Appalachians represent tracts of oceanic lithosphere obducted onto the Laurentian Margin (Dewey, 1969; Malpas and Stevens, 1979). In

Newfoundland prominent ophiolite belts occur in the Humber Zone and along the western boundary of the Dunnage Zone, the Baie-Verte Brompton Line (Figure 1.1 ). The Gander River illtramafic Belt on the eastern boundary of the Dunnage Zone (Figure 1.1) is possibly a third ophiolite occurrence (Williams, 1975). In the Humber Zone, ophiolite complexes are incorporated in allochthonous terranes formed during the Taconic Orogeny (Williams, 1975). The source of the Humber Zone ophiolites remains enigmatic, though proximity to the Dunnage Zone suggests this eastern terrane may be a possible source. Occurrences of Early Ordovician ophiolites along the Baie V erte- Brompton Line are associated with volcanic rocks of island arc affinity (Williams, 1975).

This suggests that extensive volcanic arc development occurred prior to the Taconic Orogeny (Williams, 1982). Back-arc spreading in the arcs is a possible source for creating the oceanic lithosphere represented by the ophiolite complexes. Complex structural geology, metamorphism, and poor exposure limits the extent to which this tentative link between the Dunnage and Humber zone ophiolites can be demonstrated.

Early emplacement models for the Bay of Islands Ophiolite Complex utilized gravity sliding as the primary tectonic mechanism (Rodgers and Neale, 1963, Stevens, 1970, Williams, 197 5). These models suggest that each structural slice of the allochthon slides down-slope from the east, progressively building the Humber Arm Allochthon (Williams, 1975). In order to create the potential energy required for gravity slides continuous uplift must occur in the lll,nterland of the orogen, moving each successive slice into a structurally elevated position and providing "tectonic head" (Malpas and Stevens, 1979). Furthermore, to generate a failure with displacement in a particular

direction the uplifted rock units must dip in that general direction. Sustained orogenic uplift has not been documented during the middle to late Ordovician; limiting the possibility of gravity sliding as a mechanism for the development of the regionally extensive Humber Arm Allochthon.

Malpas and Stevens (1979) proposed the concept of tectonic underplating to describe the stacking sequence of the allochthons and the styles of deformation observed in Bay of Islands. This model suggests that the Grenville basement of the Laurentian margin is subducted eastwards beneath oceanic lithosphere and the developing island arc system (Malpas and Stevens, 1979). As subduction continues foreland propagating thrust faults detach slices of the continental margin, adding the slices to the base of the obducting plate. Melange formed along the boundaries of the structural slices is considered to be due to the increase in hydrostatic pressure during the underplating process. In this fashion the structural stacking order of the Humber Arm Allochthon is created and the relative transport distances of the slices are preserved (Malpas and Stevens, 1979), not unlike the models proposed for the development of accretionary wedges (e.g., Karig, 1980; Charvet and Ogawa, 1994).

Ophiolite obduction during trench rollback is suggested by Cawood and Suhr (1992) as the primary mechanism for emplacement of Bay of Islands Ophiolite Complex.

Trench rollback requires the presence of old, heavy oceanic crust to generate high rates of subduction. Cawood and Suhr (1992) suggest that this dense oceanic lithosphere was preserved between promontories and re-entrants of the Laurentian margin. Extensional zones are created within the outboard arc complex as the obducting plate thins to keep